1，Minimum backlash

The minimum backlash is basically determined by the oil film thickness and thermal expansion.

Generally speaking, the normal oil film thickness is 1~2 μ M or so.

The backlash of the gear decreases due to thermal expansion. Take the temperature rise of 60 ℃ and the graduation circle of 60mm as an example:

The backlash of steel gear is reduced by 3 μ M or so.

The backlash of nylon gear is reduced by 30~40 μ M or so.

According to the general formula for calculating the minimum backlash, the minimum backlash is roughly 5 μ M, obviously speaking of steel gears.

Therefore, it should be noted that the minimum backlash of plastic gear is about 10 times higher than that of steel gear in terms of thermal expansion.

Therefore, when designing plastic gears, the side clearance is relatively large. The specific value shall be determined according to the specific material and the specific operating temperature rise.

If the minimum backlash is too small so that the double-sided teeth are in side contact, the contact friction between the two surfaces will increase sharply, resulting in a sharp rise in temperature and damage to the gear.

2，Tooth thickness deviation

When the tooth thickness increases, the backlash decreases, and when the tooth thickness decreases, the backlash increases.

3，Pitch deviation

This problem involves the judgment of the driving wheel and the driven wheel, and the meshing effectiveness after the tooth pitch changes, which needs to be analyzed in detail.

4，Out of roundness deviation

It is embodied in the runout of the tooth groove (tooth body). It is also negatively correlated with lateral clearance.

5，Center distance deviation

The center distance is positively related to the side clearance.

For the determination of gear design backlash, the above five factors must be considered before the appropriate backlash design value can be given.

Therefore, you cannot simply refer to the approximate side clearance value of others to determine your own design side clearance.

It can only be determined after considering the deviation value of gear accuracy and gear box center distance.

If the gearbox is made of plastic and provided by different suppliers (for example, the supplier changes), it will be difficult to determine.